Surprisingly good single track trails, in a classic second-growth forest setting. Close to Seattle, and served by Metro Transit.
How to get there:
On Mercer Island, take Island Crest Way south from I-90, to SE 68th Street. Trails are in Pioneer Park, which is located NE, NW, and SE of the Island Crest Way/SE 68th Street intersection.
A good hour-long ride if you take the outer perimeter trails; another hour to ride the rest.